CYP2D6 is a Phase I oxidative metabolism enzyme that is clinically important because about 20-25% of clinically used drug are metabolized by the CYP2D6 enzyme. CYP2D6 substrates are typically lipophilic and include drugs such as antidepressants, antipsychotics, antiarrhythmic, antiemetic, and opioids. The exact clinical effect of the polymorphism is dependent on the drug and the variant alleles expressed because individual allele variants can lead to a range of metabolic ability from ultrarapid metabolizers (UMs) to poor metabolizers (PMs). There have been 74 identified allelic variants of the CYP2D6 gene and the number seems to be increasing. Within the population there are fully functional alleles, alleles with reduced function, and non-functional alleles (null). The genotype of the individual indicates the level of enzymatic activate. The result of this polymorphism is adverse xenobiotic effects or even total lack of xenobiotic effect if a standard a dose is administered.
